The present invention relates in general to a pneumatic flotation device for use in a continuous web processing system and a method of making the pneumatic flotation device.
Numerous types of continuous web processing systems are used to process continuous flexible substrates such as paper, plastics, foils and the like. These systems are used in printing process for newspapers, photographic processes, coating processes, wrapping processes, and the like (individually and collectively referred to herein for brevity as xe2x80x9cprocessxe2x80x9d or xe2x80x9cprocessesxe2x80x9d). A continuous web processing system is referred to herein alternatively as a xe2x80x9csystemxe2x80x9d or xe2x80x9cweb systemxe2x80x9d and the flexible substrate is referred to herein alternatively as the xe2x80x9csubstrate,xe2x80x9d xe2x80x9cwebxe2x80x9d or xe2x80x9cweb material.xe2x80x9dThe scope of the present invention is not intended to be limited by such abbreviations or any other abbreviated terms used to describe the present invention, components, steps or processes thereof.
A conventional web processing system is schematically illustrated in FIG. 1. This system, generally designated numeral 10, includes an unwind mandrel 12 which supports a roll 14 of a web or substrate 16. The substrate 16 is withdrawn from the roll 14 and passes around a number of idle rollers or pulleys 18, 20, 22 and 24 (generally referred to as xe2x80x9cidlersxe2x80x9d) adjacent to a process device 26. In order for the substrate to move predictably through the system, the substrate must be under tension at all times. The process device 26 could be any device for which a continuous web processing system is used such as a rewind mandrel, printer, coater, etc., as is well understood in the art. It should also be appreciated that the various rolls and idlers are mounted to and supported by a frame 28 in the web system 10.
The above-described system 10 is provided for explanatory purposes to present a better understanding of a web system in general, and does not represent any one particular process, nor a specific number of rolls, idlers, etc. The depicted web system 10 generally represents any process involving a substrate or web material under tension, whether in the formation of the material 16 or stretching, winding or preparing the material 16 prior to, during or after printing, coating, etc.
It should also be appreciated that process device 26 in FIG. 1 generally determines the process speed and drives the web system 10. The process device 26 pulls the substrate or web material 16 off roll 14 at a predetermined speed. The roll 18 and idlers 20, 22 and 24 simply guide substrate or web material 16 through the process, rotating in response to the material""s 16 passing and directing the material through various processing devices.
Roll 18 and idlers 20, 22 and 24 guide (or steer) the web material 16 through the process prior to, during or after processing in the process device 26. While roll 18 and idlers 20, 22 and 24 do not further the web material 16 through process (i.e., do not add to the process speed), it should be appreciated that these rolls and idlers exert an inertial drag on the web. This can cause the web material 16 to gain tension, thus slowing the process or to tear, stretch or otherwise become unsuitable for subsequent processing or use. Furthermore, as the web material comes in physical contact with the rolls and idlers, imperfections on the rolls or idlers can be transferred to the web material 16 thus damaging the substrate. Rotational friction of the roller or idlers may cause irregular or undesired tension on the substrate.
To avoid these problems, continuous web processing systems have included air bars which support the flexible web material by creating a boundary layer of air. However, such systems use excessive amounts of air due to the practical limit on the minimum size of the holes in the support structure. Moreover, if the web material does not substantially cover the air bar, the air pressure within the tube becomes insufficient to maintain the necessary boundary layer of air and does not support the web. Similarly, porous structural tube are inadequate because they tend to clog with impurities from the air source and cannot be readily and inexpensively cleaned or reconditioned.
Accordingly, there is a need for a continuous web processing system which enables the substrate or web material to pass without interference or damage. In addition, there is a need for a device that enables the web material to pass through the process without destroying the material.
The apparatus and method of the present invention provides a pneumatic flotation device for use in a continuous web processing system for continuously processing paper and other flexible materials. The pneumatic floatation device of the present invention replaces the rolls and idlers currently used in such processes.
The pneumatic floatation device includes a microporous sheet mounted on, wrapped around or otherwise in contact with a suitable pneumatic support structure. The microporous sheet has a smooth exterior layer with regularly spaced pores which enable air to pass through this layer. The microporous sheet also has an interior layer attached to the interior side of the exterior layer. The interior layer includes an open weave metal fabric, or a pattern or structure of support detents that enables air to move freely along the interior side of the microporous sheet parallel to the exterior surface when the microporous sheet is in contact with the pneumatic support structure.
In one preferred embodiment, the pneumatic support structure includes a rigid tube and an airflow device in fluid communication with the microporous sheet. All or a portion of the support structure is covered with the microporous sheet to form an air boundary layer. The support structure includes spaced apart holes formed along the tube that enable air to flow through the tube to the interior side of the microporous sheet and move freely along the two axes of the sheet.
The invention further includes a method of making the microporous sheet and attaching it to the pneumatic support structure to form the pneumatic floatation device. The method includes: (i) preparing a substrate of a conductive surface suitable for electro-forming; (ii) creating a plating mask consisting of an array of small detents (with an area of 0.0001 inches or less); (iii) electro-forming a sheet of nickel (on the order of 0.002 inches) forming pores, apertures or voids in the areas of the small detents; (iv) wrapping a sheet of wire cloth or fabric onto the sheet of metal and the plating mask; (v) electroplating the wire cloth or fabric onto the sheet of metal; and (vi) attaching the microporous sheet to the support structure.
It is therefore an object of the present invention to provide a pneumatic flotation device for continuous web processing systems.
A further object of the present invention is to provide a method of making a pneumatic floatation device for continuous web processing systems.
A still further objective of the present invention is to provide a pneumatic flotation device that enables a substrate or web material to predictably move through a continuous web processing system without contacting or driving the idlers.
Other objects, features and advantages of the invention will be apparent from the following detailed disclosure, taken in conjunction with the accompanying sheets of drawings, wherein like numerals refer to like parts, components and processes.